There is an increasing need in modern technology for high surface area, rapidly soluble, hydrated alkali metal silicate solid materials. Such products find utility as binders for "gunning mixes" of refractory powders. In steel making furnaces such as basic oxygen furnaces, open hearth furnaces, and electrical furnaces, erosion occurs in particular areas of the furnace due to a combination of heat, chemical corrosion, and the abrasive solid materials which are melted in the furnace. Prior to the advent of suitable patching compounds called gunning mixes, it was necessary to halt production of these furnaces and rebuild them when this erosion proceeded to a substantial degree. Now, however, these furnaces can be patched with refractory grain which is shot into the molten furnace along with a binder in aqueous solution. This mixture adheres to the walls and patches the eroded areas, thus avoiding the necessity of furnace shutdown. In many instances a high rate of solution of the binder in water is critical since the dry binder powder is shot through a nozzle and sprayed with water immediately as it leaves the nozzle. The powder wet by water is propelled by air pressure into the white-hot furnace and hits the walls where it adheres to form the patch. It is vital for the success of this operation that the binder sodium silicate go into solution with extreme rapidity, since the total contact time is exceedingly short. While existing sprayed-dried hydrated sodium silicates perform reasonably well in this application, an even more rapidly soluble powder is desired.
In another application, modern detergent formulations which do not contain phosphate, do contain much larger quantities of nonionic surfactants than previous phosphate formulations. Nonionic surfactants are desirable in such applications, since they are not sensitive to the calcium and magnesium ions present in hard waters and are not precipitated or inactivated by them. It is difficult, however, to supply the nonionic surfactant by spray drying in a spray-drying tower, as is conventional with formulating detergent compositions. This is because the liquid nonionic is steam distilled by the water in the mixture which is sprayed-dried and escapes from the composition creating a severe air pollution problem. There is therefore a need for highly absorbent powders, preferably of constituents which would normally be present in detergents, and which are ecologically acceptable. Thus, highly absorbent alkali metal silicate powders can be very helpful in formulating such compositions by allowing the nonionic detergent to be absorbed into its structure. Subsequently, the carrier silicate can be post-blended with the other constituents which have been spray-dried, thereby avoiding putting the nonionic liquid through the spray tower and thus avoiding air pollution. Unfortunately, existing water-soluble alkali metal silicate powders such as spray-dried sodium silicate, have little or no absorbency.
Finally, it is desirable to prepare very low bulk density refractory powders of silica for use as catalyst supports and as insulating materials.
Existing hydrated alkali metal silicates, such as spray-dried sodium silicate, have large particle sizes; low porosity, relatively low surface area, ranging around one square meter per gram; a relatively high bulk density ranging around 0.6 gram/cc. and a low absorbency. Such materials generally absorb a maximum of only 10 percent by weight of nonionic surfactant without experiencing typical caking problems.
Canadian Pat. No. 917,884 issued on Jan. 2, 1973 to Robert H. Sams et al., discusses a method for making crystallized alkaline sodium silicates by reacting silicon with water in the presence of alkaline sodium silicate to produce hydrogen and form bubbles in the crystallizing mass. Even when such a process is used, the absorbency of the silicate product is only about 3.3 percent of its weight.
Techniques for agglomerating discrete particles of spray dried sodium silicate powders into aggregates having a somewhat larger size and lower bulk density have been described, for example, in U.S. Pat. No. 3,687,640 issued on Aug. 29, 1972 to Robert H. Sams et al. Although such techniques do lead to agglomeration and cause some reduction in bulk densities, the surface area and rate of solution are not thereby increased, nor are the bulk densities lowered sufficiently since bulk densities of less than 0.3 g./cc. are not thus attained.
Grinding hydrated sodium silicate glasses is another technique employed to prepare sodium silicate powder. However, because of the somewhat plastic nature of sodium silicate, it is difficult to prepare finely divided hydrated sodium silicate when a grinding technique is used. In addition, a silicate thus produced tends to be dense and irregular, typically having high bulk densities on the order to 1 to 1.4 g./cc. and an absorbency of only about 10 percent by weight based on its own weight of nonionic detergents before caking occurs.
U.S. Pat. No. 3,177,147 issued on Apr. 6, 1965 to B. B. Dugan discloses the preparation of complex detergent compositions which may contain sodium silicate. In the method outlined, a completed detergent formulation is mixed with water and an oxygen-liberating compound to form a paste capable of retaining small oxygen bubbles without coalescing. Minimal mixing is carried out in order to lose as little of the oxygen from the per compound as possible from the paste mass. The oxygen is liberated from the per compound in sufficient amounts to both bleach and expand the paste until the paste is at least twice its initial volume. The paste is allowed to set by the absorption of water to make hydrates of the various builder and filler salts such as sodium sulfate and sodium phosphate which are introduced in an anhyrous form or in a lower state of hydration. The set paste is a friable mass which is then granulated. Such a process for treating detergent compositions does not yield excellent results when used with a sodium silicate alone since silicates tend to agglomerate once they lose their free-flowing state and form a paste. As a result, the mass or heat transfer necessary to cause the evolution of volatiles (H.sub.2 O and H.sub.2 O.sub.2) becomes impossible, particularly at a sufficiently rapid rate to avoid non-uniform, relatively non-porous structures. In such instances, water can be removed rapidly at the surface of such a large coalesced mass of material, but the anhydrous skin which forms is a very good insulating barrier to minimize further heat and mass transfer. Under such conditions, it is found that one may heat for hours, achieving a completely anhydrous outer surface, while the interior of the expanded structure is still moist. Not only is such a highly heterogeneous structure undesirable in terms of product uniformity, but rates of drying overall are quite slow and the competing process of sintering proceeds to an excessive degree, forming a product with an unsatisfactory amount of absorption.
Other methods for using hydrogen peroxide and silicates in other complex formulations have been disclosed in the prior art. British Patent No. 996,563 issued on June 30, 1965 to Bedrich Cibulka, for example, discloses a method for preparing pre-cast building materials wherein a silicate, an inert inorganic filler, a hardening agent to accelerate the setting of the mixture, hydrogen peroxide, elementary iron and a copolymer are fashioned into a paste and shaped in a mold. Such a process yields a water insoluble material that is useless in detergent formulations. The product is also devoid of residual binding affinity and unless as a gunning mix. Clearly, the product is not as amorphous silicate.